AR and prostate cancer: The authors confirmed that in mice and patients with prostate cancer, abiraterone is converted to the more active Δ4-abiraterone (D4A), which inhibits CYP17A1, 3βHSD, and steroid-5α-reductase (SRD5A), required for DHT synthesis, and then antagonizes the androgen receptor, providing an additional explanation for the clinical abiraterone activity.